The present invention relates to a method and apparatus for blow molding plastic drinking vessels including the formation of a bead around the rim thereof with smooth finishes on both the interior and exterior surfaces thereof. More specifically, the present invention relates to a method and apparatus for blow molding a plastic drinking glass and forming a bead around the rim thereof having a sufficient projection on the exterior surface to accommodate and retain a snap-on plastic lid for sealing the drinking glass.
A need in the art exists for a plastic drinking glass with a suitable bead structure around the rim thereof which permits the drinking glass to be sealed such as by a snap-on plastic lid and sold as a carry-out beverage package in a fast food type restaurant. It would be particularly advantageous to provide such a package for use in drive-through serving sections of fast food restaurants.
Clearly, it is desirable to package beverages in the most attractive of packages and of course it is generally accepted that real glass drinking vessels are considered to be the most attractive and aesthetically pleasing for the consumer. However, real glass is heavy, expensive, and fragile and, therefore, impractical for use as a carry-out beverage package. Plastic, on the other hand, can be made to look as good or better than glass and it is safer, lighter, and cheaper than glass. In addition, it has the ability to be inexpensively recycled, which has both economical and environmental advantages.
However, in order to be practical for use as a carry-out beverage package, a plastic glass needs to be capable of possessing all of the functional attributes of a paper cup such as the provision of a bead around the rim which will accommodate a snap-on plastic lid for sealing of the vessel.
Because a plastic glass can be made of transparent materials, such as polycarbonate or PETG, it can be made to simulate the appearance of a transparent, real glass. It can also be provided with attractive graphics and used for product promotions. However, if used in this manner it is still desirable to keep the production costs to a minimum to ensure a cost effective promotion.
Heretofore, plastic promotional cups or vessels have primarily been injection molded which is often functionally limiting process.
Ideally, a plastic drinking glass should be blow molded for cost savings. However, the resulting plastic drinking glass formed from a blow molding process must have a smooth inner rim area for comfort of the consumer's lips while drinking therefrom. It must also have a smooth outer surface for the rim or bead which has a large enough projection to accommodate a snap-on plastic lid as stated hereinbefore.
Traditionally, blow molding of containers such as jars which have an external bead which is formed by the recess in the blow mold do not have a smooth inner surface around the rim because the cutting process for severing the molded article from its parison tends to leave a rather rough, sharp inner surface area around the rim. Of course if the container is to be used as a jar such as for storage of various contents, and it is not to be used as a drinking vessel, it is acceptable to leave a fairly rough inner finish around the interior of the rim.
However, a need in the art exists for a blow molding process and apparatus which can provide a smooth inner surface for the rim, making the blow molded container suitable for use as a drinking vessel having the appearance of transparent glass.
However, for cost savings, it would be desirable that the entire process which forms the smooth inner surface around the rim of the vessel, takes place within the blow mold so that no external secondary processing is required to achieve the smooth inner surface or bead.
In the alternative, if any external secondary processing is needed in order to achieve this smooth inner surface, it is desirable that it be as simple as possible to help keep additional processing costs at a minimum.